Render pass that output center of object of each pixel
You can do this by using a Material Override and a special material to give the objects' positions.

First create a new material with an emission shader (you can add it to any object, it doesn't matter).  Add an Input > Object Info node and plug the Location into the color of the emission shader.



Now you can create a fake user for the material and remove it from whatever object you added it to.

Then add a new render layer and set the Material Override (under the Layer rollout) to the material you just created.  It would also be useful to override the samples to 1 as well to reduce rendertimes and effectively disable antialiasing.



In the resulting RAW rendered image the red, green, and blue values of each pixel will represent the location of the object rendered on that pixel.